Conventionally a terminal of an information appliance is connected with a LAN constructed in an office and a homes. A plurality of LANs is connected with each other with gateways (relay connection unit). The gateway has relay processing information (routing information) indicating a LAN to which a received message is relayed.
In each LAN, a system construction such as the disposition of the terminal of the information appliance, the number of the terminals thereof, and the like is arbitrarily altered. Thus in the gateway (relay connection unit) connected with the LANs, various methods of managing the routing information of altering the relay processing information in correspondence to the change of the system construction have been proposed.
For example, disclosed in Japanese Patent Application Laid-Open No. 7-273787 (Patent document 1) is a method of managing the routing information of discriminating whether a message transmitted from each terminal is a message for relay or for altering the relay processing information and executing a series of processing reconstructing the relay processing information for routing use by using a dedicated processor if the message is for altering the relay processing information. That is, in general networks, as methods of dynamically generating the relay processing information, a message for altering the relay processing information is sent and received by using a dedicated protocol such as a RIP (Routing Information Protocol), an OSPF (Open Shortest Path First), and a BGP (Border Gateway Protocol).
In a car, a plurality of LANs including CAN mounted on a vehicle is constructed, and the LANs are connected with one another by means of the relay connection unit.
In the LAN system mounted on the vehicle, the dispositions of electronic control units to be connected with the LAN mounted on the vehicle are set. Normally the connection state of each electronic control unit is not altered.
Therefore the relay connection unit in the LAN system mounted on the vehicle beforehand stores the relay processing information (routing information) showing an electronic control unit to which a received message is relayed as a program and does not generate the relay processing information unlike the LAN system constructed in offices and homes.
In the LAN system mounted on the vehicle, basically a message is broadcast and the destination of the message is not fixed unlike the general LAN system in which uni-cast is performed. Therefore an established protocol for constructing the relay processing information for relaying a message is not present in the LAN system mounted on the vehicle. Thus the LAN system mounted on the vehicle has an aspect that it is incapable of generating the relay processing information.
Patent document 1: Japanese Patent Application Laid-Open No. 7-273787